1. Field of the Invention
This invention relates generally to breath training techniques, and more particularly to an apparatus and method for monitoring the respiratory sinus arrhythmia as a biofeedback tool during various breathing training techniques.
2. Description of Related Art
It is known that the autonomic nervous system (ANS) regulatory mechanism has an influence on various organs and systems of the human body. The system works as a highly complex set of interacting physiological oscillators. One of the main functions of the ANS is to maintain an optimum balance between those oscillators. Any prolonged regulatory imbalance may cause functional disorders eventually debilitating the entire human organism. One of the major causes of such imbalance is psycho-emotional stress. There are many techniques that claim a means for stress reduction, which provides a positive effect on the ANS regulatory function. The goal of such techniques is to switch the ANS into a specific "resonant" state characterized by a synchronous, smooth, coherent, sine-like pattern of oscillations of many physiological parameters, e.g. heart rate (HRT), blood pressure (BP), breathing rate (BR), pulse wave propagation time (PWPT), and so forth.
A good example of resonant state phenomena is the respiratory sinus arrhythmia pattern (RSA), where HRT is oscillating synchronously to the breathing cycle. Since one of the goals of stress reduction techniques is to increase the resonance between oscillating physiological parameters, it is important to be able to dynamically evaluate a quantitative measure of the significance and stability of the resonant pattern and establish feedback to reinforce the positive changes.
Some key facts are worth noting:
1. There are numerous well-known breathing techniques used in clinical rehabilitation, stress management, sports and fitness training, alternative medicine and Yoga, etc. PA0 2. The positive effect of breathing exercises is related to the influence of breathing on the sympato-vagal neuro-regulation of cardiovascular system. Two branches of the autonomic nervous system (sympathetic and parasympathetic) have their antagonistic effects on the heart, blood vessels and all other systems and organs of the human body. One of the predicates of well being is to learn how to maintain an optimal balance between these two branches of the regulatory mechanism. PA0 3. Heart rate variability (HRV) has been recognized as a key marker that reflects the condition of both the sympathetic and parasympathetic nervous systems and their balance. HRV indicates how the time between consecutive heartbeats (interbeat intervals) varies. This variability has a direct effect on the two branches of autonomic nervous regulation. PA0 4. It has been noted and supported by numerous research studies that breathing causes a specific pattern of heart rate variability called respiratory sinus arrhythmia (RSA). Normal breathing has a fairly stable pattern described by respiration rate, volume of breathing, lengths of all components of breath cycle (inhalation, exhalation, pauses at the end of inhalation and exhalation). The RSA effect produces a pattern of variations of heartbeats synchronous to the breath cycles. PA0 5. Normal (tidal) breathing causes noticeable RSA patterns in relatively healthy human subjects. Its significance is decreased with age, conditions of stress, depression, panic, anxiety and many other functional and psychosomatic disorders. PA0 6. Various breathing exercises that alter breath patterns increase the significance of the RSA pattern. This effect is considered as a reflection of the healing mechanism of the breathing exercise, which causes a positive influence or harmonization of both the sympathetic and parasympathetic nervous regulation. PA0 7. Providing subjects with the means to maintain a specific breathing pattern results in an increase of the RSA effect followed by positive changes in HRV parameters. This change is a direct indicator of the normalization of sympato-vagal regulation of the overall organism.
To conduct HRV analysis and particularly evaluate the RSA pattern an electrocardiograph (ECG) signal is usually measured. The interbeat intervals are derived from the ECG as the intervals between consecutive R-peaks. This method is very accurate and reliable but has a significant disadvantage: namely, it requires the use of complex and expensive ECG equipment with multiple electrode placements on the wrists or the chest. An alternative is to use a photoplethysmograph (PPG) measurement by means of a portable and convenient finger sensor. The PPG sensor emits an infrared (IR) light on the skin. The emitted light is partially consumed by the blood flow. The degree of light consumption/reflection is proportional to the changes in blood flow. The PPG signal has periodic peaks that represent blood vessel pulsation. It can be also used to derive the interbeat intervals representing the time between two PPG peaks.